BERLIN (AP).- A court has ruled that a Jewish man whose father lost his collection of thousands of rare posters to the Nazis can't demand their return from a German museum, it said Friday.

A Berlin appeals court said it ruled that while Peter Sachs, the son of collector Hans Sachs, is the owner of the posters, now worth millions, he isn't entitled to their restitution by the government-owned German Historical Museum. The court did not immediately explain its reasoning behind the decision.

The Thursday ruling partly reversed one by a lower court last year that said the museum must return a poster for "Simplicissimus," a satirical German weekly magazine, showing a red bulldog.

The case was a test of Sachs' claim to the 4,300 surviving posters held by the museum, now worth at least euro4.5 million ($6.3 million).

The lower court found that Hans Sachs never gave up ownership of the collection of 12,500 posters taken from his home on the Nazis' orders in 1938. His family fled to the U.S. shortly after that year's anti-Jewish Kristallnacht, or Night of Broken Glass, pogrom.

At a hearing on Thursday before its ruling on a museum appeal, appeals court judge Rainer Bulling raised the possibility that a 1961 compensation payment of 225,000 German marks (then worth about $50,000) from the West German government to Hans Sachs may be a legal obstacle to restitution, among other factors.

It wasn't immediately clear when a full written ruling would be available.

"We will study the reasons for the decision and then decide what legal measures we can take against this ruling," said Sachs' German lawyer, Matthias Druba.

He said that, independent of any further legal steps, he hopes the German government will "do the right thing" and help reach a "fair solution" to the case.

Sachs, of Sarasota, Florida, is glad that his ownwership was upheld, but "of course he is very disappointed that German courts say they can't help him assert ownership," Druba said.

German Historical Museum spokesman Rudolf Trabold had no immediate comment, saying that officials would first examine details of the ruling.

Peter Sachs has argued that the original compensation was paid when it appeared the collection was destroyed in World War II, and that once his father found out part of it had survived, he started trying to get access to it in the East German museum where it ended up.

Hans Sachs learned five years after accepting compensation that part of the collection was in East Berlin. He wrote in vain to communist authorities about seeing the posters; and died in 1974 without ever seeing them again.

The collection was given to the German Historical Museum in 1990, after reunification.

Peter Sachs says he only learned of the collection's existence in 2005, and began fighting then for the return of the posters.

A German restitution panel ruled in 2007 that the museum was their rightful owner.